Journal of Energy Bioscience 2024, Vol.15, No.2, 85-95 http://bioscipublisher.com/index.php/jeb 89 electron transfer processes. In one study, the introduction of FePc into a carbon cloth electrode significantly enriched the Geobacter population in the EAB, increasing their abundance from 6.97% to 44.83% (Li et al., 2021). This enrichment led to a substantial increase in power density and biomass loading, demonstrating the effectiveness of Geobacter in DET (Li et al., 2021). Another study highlighted the role of Geobacter in a neutral red-mediated MFC, where the addition of neutral red enhanced the electron transfer and induced the growth of exoelectrogens, including Geobacter (Chen et al., 2021). This resulted in improved MFC performance, showcasing the potential of Geobacter in bioelectrochemical applications (Chen et al., 2021). Overall, the ability of Geobacter species to efficiently transfer electrons directly to electrodes makes them ideal candidates for enhancing the performance of MFCs and other bioelectrochemical systems. Their well-characterized DET mechanisms provide valuable insights into the design and optimization of these systems for sustainable energy production and environmental remediation (Zhao et al., 2020; Chen et al., 2021; Li et al., 2021; Paquete et al., 2022). 5 Mediated Electron Transfer (MET) Mechanisms 5.1 Use of redox mediators in electron transfer Mediated Electron Transfer (MET) in microbial fuel cells (MFCs) involves the use of redox mediators to facilitate the transfer of electrons from electroactive bacteria to the anode. Redox mediators are compounds that can shuttle electrons between the microbial cells and the electrode, thereby enhancing the efficiency of electron transfer. These mediators can be either naturally secreted by the bacteria or artificially added to the system. Natural redox mediators include compounds like flavins and pyocyanins, which are secreted by certain bacteria to facilitate electron transfer (Aiyer, 2019). Artificial mediators, such as methylene blue and neutral red, are often added to MFCs to improve electron transfer rates and overall system performance (Kalathil et al., 2016; Aiyer, 2019). The use of redox mediators is crucial in overcoming the limitations posed by the cell envelope and the low redox potential difference between the intracellular and extracellular environments. By acting as electron carriers or bridges, these mediators enable efficient extracellular electron transfer (EET), which is essential for the operation of MFCs. The efficiency of MET is influenced by the redox potentials of the mediators and the microbial oxidative metabolism that liberates electrons (Aiyer, 2019). 5.2 Identification of natural and synthetic mediators Natural redox mediators are typically produced by electroactive bacteria as part of their metabolic processes. For instance, Geobacter sulfurreducens and Shewanella oneidensis are known to produce flavins and other redox-active compounds that facilitate electron transfer to the anode (Logan et al., 2019; Zhao et al., 2020). These natural mediators are advantageous because they are inherently biocompatible and can be continuously produced by the bacteria, reducing the need for external additions. Synthetic mediators, on the other hand, are externally added compounds that can enhance the electron transfer capabilities of MFCs. Common synthetic mediators include methylene blue, neutral red, and various quinones (Kalathil et al., 2016; Aiyer, 2019). These compounds are selected based on their redox potentials and their ability to interact with the microbial cells and the electrode surface. The use of synthetic mediators allows for greater control over the electron transfer process and can significantly improve the performance of MFCs. 5.3 Case Studies illustrating MET in Various MFC configurations Several case studies have demonstrated the effectiveness of MET in different MFC configurations. For example, a study on the use of iron phthalocyanine (FePc) modified carbon cloth (CC) electrodes showed that the modification significantly improved the viability of electroactive biofilms and enhanced electron transfer rates (Li et al., 2021). The FePc-CC anode achieved a much higher power density and biomass loading compared to unmodified CC, highlighting the potential of using synthetic mediators to boost MFC performance.
RkJQdWJsaXNoZXIy MjQ4ODYzMg==